In order to increase bandwidth in data connections provided to subscribers of a telecommunications network operator, such operators are providing greater amounts of optical fiber connections in their access networks (e.g. as in an FTTC architecture). Generally speaking, the shorter the copper pair connection over which a signal is to be transmitted the greater the bandwidth that can be supplied over that connection (because as the connection reduces in length so the frequency at which signals can be successfully transmitted over that connection tends to increase). To take advantage of the higher frequency signals which can be transmitted over relatively short copper pair connections, higher bandwidth DSL standards have been developed. An important such standard is the Very-high-bit Digital Subscriber Line (VDSL) standard, the most up-to-date version of which is currently set out in the ITU standard G993.2 and is commonly referred to as VDSL2.
One feature which it would be desirable to include in this standard is a set of one or more low power modes. Such low power modes have already been introduced into the most recent Asynchronous DSL (ADSL) standard (see ITU G992.5—the ADSL 2+ standard). The aim of a low power mode is to enable a DSL connection to substantially reduce the amount of power required by the connection when no or very little data is being transmitted over the line, whilst enabling the connection to automatically and relatively quickly return to its normal high bandwidth mode whenever there is data for transmission over the connection. An ideal low power mode draws very little power when it is in the low power mode but can very quickly re-establish to the normal high bandwidth mode as soon as there is a demand for high bandwidth.